audio-extractor: Uses ffmpeg to extract the audio from a video file.

audio-extractor.sh

#!/bin/bash

assert_is_numeric()
{
    re='^[0-9]+$'
    if ! [[ $1 =~ $re ]] ; then
        echo "Error: Value '$1' is not a number" >&2; exit 1
    fi
}

declare -a req=("ffmpeg" "ffprobe" "basename" "grep" "sed")

for cmd in "${req[@]}"
do 
    command -v $cmd >/dev/null 2>&1 || { echo "Required command not found: $cmd"; exit 1; }
done

start=0
trim=0

while getopts ":s:e:" opt; do
  case $opt in
    s)
      start=$OPTARG
      assert_is_numeric "$start"
      ;;
    e)
      trim=$OPTARG
      assert_is_numeric "$trim"
      ;;
    :)
      echo "Option -$OPTARG requires an argument." >&2
      exit 1
      ;;
  esac
done
shift $(expr $OPTIND - 1 )

#[ $1 ] || { echo "Usage: $0 file1 [file2]..."; }

for i in "$@"
do
    [ -f "$i" ] || { echo "File $i not found!"; exit 1; }
done

echo ""
echo "Trimmed from start : ${start} seconds"
echo "Trimmed from end   : ${trim} seconds"
echo ""

for file in "$@"
do
    echo "======================================================="

    if [ -f "$file" ]; then
        infile=$(basename "$file")
        outfile="${infile%.*}.m4a"
        
        echo -e "\nProcessing '$infile'\n"

        if [ ! -f "$outfile" ]; then
            duration=$(ffprobe -i "$infile" -show_entries format=duration -v quiet | grep "duration" | sed -e "s/duration=//" | sed "s/\..*$//")
            tduration=$((duration-start-trim))
            
            echo "Initial Duration   : $duration seconds"
            echo "Target Duration    : $tduration seconds"

            # Extract audio from video.
            ffmpeg -ss $start -t $tduration -i "$infile" -map 0:a -c copy "$outfile" -v quiet
            echo -e "\nExtracted audio to '$outfile'"
        else
            echo "File '$outfile' already exists."
        fi

    else
        echo "File '$file' not found."
    fi

    echo ""
done